1. Field of the Invention
This invention relates to interconnection schemes for use primarily with telecommunication devices such as patch cords or cable assemblies. More particularly, this invention relates to an electrically, balanced connector assembly and to an assembly fixture for fabricating the connector assemblies and patch cord assemblies.
2. Description of the Prior Art
Communication system and/or network efficiency is directly dependent upon the integrity of the connector scheme employed. Such connector schemes include, for example, standard interfaces for equipment/user access (outlet connector), transmission means (horizontal and backbone cabling), and administration/distribution points (cross-connect and patching facilities). Regardless of the type or capabilities of the transmission media used for an installation, the integrity of the wiring infrastructure is only as good as the performance of the individual components that bind it together and to the way in which these components are assembled.
By way of example, a non-standard connector or pair scheme may require that work area outlets be rewired to accommodate a group move, system change, or an installation with connecting hardware whose installed transmission characteristics are compatible with an existing application but are later found to have inadequate performance when the system is expanded or upgraded to higher transmission rates. Accordingly, connecting hardware without properly qualified design and transmission capabilities, can drain user productivity, compromise system performance and pose a significant barrier to new and emerging applications.
Reliability, connection integrity and durability are also important considerations, since wiring life cycles typically span periods of ten to twenty years. In order to properly address specifications for, and performance of telecommunications connecting hardware, it is preferred to establish a meaningful and accessible point of reference. The primary reference, considered by many to be the international benchmark for commercially based telecommunications components and installations, is standard ANSI/EIA/TIA-568 (TIA-568) Commercial Building Telecommunications Wiring Standard. A supplement Technical Systems Bulletin to TIA-568 is TIA/EIA TSB40 (TSB40), Additional Transmission Specifications for Unshielded Twisted-Pair Connecting Hardware. Among the many aspects of telecommunications wiring covered by these standards are connecting hardware design, reliability and transmission performance. Accordingly, the industry has established a common set of test methods and pass/fail criteria on which performance claims and comparative data may be based.
To determine connecting hardware performance in a data environment, it is preferred to establish test methods and pass/fail criteria that are relevant to a broad range of applications and connector types. Since the relationship between megabits and megahertz depends on the encoding scheme used, performance claims for wiring components that specify bit rates without providing reference to an industry standard or encoding scheme are of little value. Therefore, it is in the interest of both manufacturers and end users to standardize performance information across a wide range of applications. For this reason, application independent standards, such as TIA-568 and TSB40, specify performance criteria in terms of hertz rather than bits. This information may then be applied to determine if requirements for specific applications are complied with. For example, many of the performance requirements in the IEEE 802.3 (10BASE-T) standard are specified in megahertz, and although data is transmitted at 10 Mbps for this application, test "frequencies" are specified in the standard (as high as 15 MHZ).
Transmission parameters defined in TSB40 for unshielded twisted pair (UTP) connectors include attenuation and near-end crosstalk (NEXT) and return loss.
Connector attenuation is a measure of the signal power loss through a connector at various frequencies. It is expressed in decibels as a positive, frequency dependent value. The lower the attenuation value, the better the attenuation performance. Attenuation may be defined as a measure of signal power loss due to the connecting hardware and is derived from swept frequency voltage measurements on short lengths of 100-ohm twisted pair test leads before and after splicing-in the connector under test. The worst case attenuation of any pair within a connector shall not exceed the values listed below in TABLE I, where for Category 5, the values correspond approximately with attenuation that is equivalent to a 2 meter cable,
TABLE I ______________________________________ UTP Connecting Hardware Attenuation Frequency Category (MHZ) (dB) ______________________________________ 1.0 0.1 4.0 0.1 8.0 0.1 10.0 0.1 16.0 0.2 20.0 0.2 25 0.2 31.25 0.2 62.5 0.3 100 0.4 ______________________________________
Connector crosstalk is a measure of signal coupling from one pair to another within a connector at various frequencies. Since crosstalk coupling is greatest between transmission segments close to the signal source, near-end crosstalk (as opposed to far-end) is generally considered to be the worst case. Although measured values are negative, near-end crosstalk (NEXT) loss is expressed in decibels as a frequency dependent value. The higher the NEXT loss magnitude, the better the crosstalk performance. Near-end crosstalk loss, the more significant problem, may be defined as a measure of signal coupling from one circuit to another within a connector and is derived from swept frequency voltage measurements on short lengths of 100-ohm twisted-pair test leads terminated to the connector under test. A balanced input signal is applied to a disturbing pair of the connector while the induced signal on the disturbed pair is measured at the near-end of the test leads. In other words, NEXT loss is the way of describing the effects of signal coupling causing portions of the signal on one pair to appear on another pair as unwanted noise. This will become more clear in a description of the test data which appears in TABLE III. In any case, the worst case NEXT loss, see values below in TABLE II, for any combination of disturbing and disturbed pairs is determined by the formula: EQU NEXT(F). .gtoreq..NEXT (16)-20 Log (F/16)
where NEXT (16) is the minimum NEXT loss at 16 MHZ, F is frequency (in MHz) in the range from 1 MHZ to the highest referenced frequency, and NEXT (F) is the performance at that frequency.
TABLE II ______________________________________ UTP Connecting Hardware NEXT Loss Limits As Specified in EIA/TIA Document TSB-40 Frequency Category 5 (MHZ) (dB) ______________________________________ 1.0 &gt;65 4.0 &gt;65 8.0 62 10.0 60 16.0 56 20.0 54 25 52 31.25 50 62.5 44 100 40 ______________________________________
Connector return loss is a measure of the degree of impedance matching between the cable and connector. When impedance discontinuities exist, signal reflections result. These reflections may be measured and expressed in terms of return loss. This parameter is also expressed in decibels as a frequency dependent value. The higher the return loss magnitude, the better the return loss performance.
Since connecting hardware is generally considered to be electrically short relative to signal wavelengths, return loss requirements are only applied to products that have lengths of internal wiring or circuitry of six inches or more (such as patch panels).
The net effect of these parameters on channel performance may be expressed in signal-to-noise ratio (SNR). For connecting hardware, the parameter that has been found to have the greatest impact on SNR is near-end crosstalk.
Several industry standards specify multiple performance levels of unshielded twisted pair (UTP) cabling components have been established. For example, Category 3, 4 and 5 cable and connecting hardware are specified in EIA/TIA TSB-36 & TIA/EIA TSB40 respectively. In these specifications, transmission requirements for Category 3 components are specified up to 16 MHZ. Category 3 will typically be applicable for transmission rates up to 10 Mbps, such as 4 Mbps Token Ring and 10BASE-T.
Transmission requirements for Category 4 components are specified up to 20 MHZ. Category 4 will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 16 Mbps, such as Token Ring.
Transmission requirements for Category 5 components are specified up to 100 MHZ. They are expected to support UTP voice as well as emerging video and ANSI X3T9 series data applications with transmission rates up to 100 Mbps, such as 100 Mbps Twisted-Pair Physical Media Dependent (TP-PMD).
In order for a UTP connector to be qualified for a given Performance category, it must meet all applicable transmission requirements regardless of design or intended use. The challenge of meeting transmission criteria is compounded by the fact that connector categories apply to worst case performance. For example, a work area outlet that meets Category 5 NEXT requirements for all combinations of pairs except one, which meets Category 3, may only be classified as a Category 3 connector (provided that it meets all other applicable requirements).
In a recent development that utilizes a load bar insert for use with a modular plug, while offering improved performance at Category 5 levels, a performance level known in the art, was introduced by Stewart Connector Systems, Inc. of Glen Rock, Pa. They introduced a Category 5 performing modular plug utilizing a sliding wire management bar, where such bar contains two rows, each with four through holes, to receive the standard eight wires of a cable. To use the management bar, the user is advised to arrange the wires in two equal sets, and cut each set of four at a 45 degree angle such that no two wires are of the same length. With the prepared wires, the wires are individually fed into the holes of the wire organizer, in sliding engagement therewith, then trimmed to the same length. For the loading step, the wire organizer is first pushed to the end of the trimmed wires, then inserted into the connector housing. In the fashion of U.S. Pat. No. 4,601,530, when the wire organizer can no longer move forward, the wires are pushed beyond the wire organizer into a position to be individually terminated, as known in the art. While claiming to provide Category 5 performance, the assembly and termination of the modular plug is very labor intensive. This prior art approach also requires the use of long and short terminals, because adjacent wires are no longer side by side when terminated. Therefore standard modular plug electrical connectors cannot be used for this approach.
Prior art RJ-45 modular plugs can be used for Category 5 patch cord assemblies. AMP Incorporated manufactures and sells 100 ohm and 150 Category 5 unshielded and shielded patch cord assemblies. These commercially available patch cord assemblies are fabricated by hand and loading bar inserts or simple separator inserts are not employed. The manufacturing yield for these prior art cables is quite low. Operators find it difficult to manipulate the short cable ends required to maintain Category 5 performance. Unsatisfactory performance may be caused when the lay or relative orientation of the twisted pair wires in a Category 5 cable is altered by "milking" the wires to simplify termination. The nonsequential orientation of Orange/White and White/Orange wires also causes assembly problems and introduces near end crosstalk problems. Thus even though the cable and the connectors may separately meet Category 5 performance specifications, the assembled patch cord does not meet those specifications.
In a companion patent application, filed concurrently with this application's parent application by one of the inventors hereof, where such companion application was assigned U.S. Ser. No. 08/332,218, an improved load bar insert is disclosed. The invention thereof, where the application is incorporated herein in its entirety, relates to an electrical connector, preferably a modular plug. A preferred embodiment of the invention of said companion application comprises a dielectric housing having a conductor receiving end, a conductor terminating end, a passageway communicating internally between the respective ends, and a spacing insert in the passageway to receive a plurality of conductors and to position same in a manner to achieve Category 5 performance levels in the modular plug. The insert is characterized by having an upper surface and a lower surface to receive or position selected pairs of the conductors. Within the limits of the housing, the insert maximizes the separation of the selected pairs and arranges them in plural planes before being realigned into a common plane for termination at the conductor terminating end. A first embodiment includes grooves in the upper and lower surfaces of the insert, while a second embodiment is directed to a rod like member, such as may be made of an elastomer, styrofoam, or plastic tube. A feature of this companion invention is the provision of separating the wires into plural planes, then bringing them together for loading into the modular plug. By incorporating the method of this invention, improved performance levels are ensured in a timely and cost efficient manner.
The procedure by which this invention supports the performance and loading of the modular plug of the companion application, and its ability to generally improve the speed in which modular plugs may be factory terminated, will become apparent in the description which follows, particularly when read in conjunction with the accompanying drawings.